I'm all for magnetic plugs, as long as they fit like stock and don't screw up threats of course. Magnetic plugs are used on each scavange line for each bearing on Jet engines. Some engines such as T700-701C on Black Hawks have "fuzz burn" which is an electrical current running through it to burn off any light fuzz from bearings. If it doesn't burn it off, it'll set off a caution light which alerts us of a larger problem (possible bearing failure). Wouldn't that be a cool thing to have in our M3's.
Anyway, filters should catch all that material but filters are designed to filter oil/fuel before it goes to the bearing/fuel nozzles. So fluid returning is where a magnetic plug would catch it. Of course in our engines, it's a different design but a magnetic plug in the oil pan/diff. I think would work well. Just me 2Ct's.